Monolith Catalyst Supports for Hydrogen Production

Mzolo, Ntokozo

Monolith Catalyst Supports for Hydrogen Production

Master Thesis

2021

Abstract

Due to increasing energy demands and environmental concerns, more research studies arc conducted on alternative energy sources. Hydrogen fuel cells arc one of the desired alternatives. The CCT Catalysis Institute has demonstrated the entire hydrogen production process from propane (LPG) reforming. This is aimed for off-grid and backup pOver supply to rural areas and telecommunication towers respectively. The steam reforming unit employs ruthenium supported on gamma-alumina (Ru/ -AbOo) catalyst.. However, it has been observed that. upon increasing the sea.le, pressure-drop and mass transfer limitations become significant issues. It is, therefore, desired to shift from packed bed reactors to monolithic reactors to overcome these issues. :Vfonoliths arc attractive due to their high open frontal area., stability, good mass and heat transfer, as well as easy sea.ling up. The main focus of this study is to coat. monoliths ,vith a. homogeneous and stable layer of Ru/ AbO3. Viscosity, pH and slurry solid content are investigated as these are the main factors affecting washcoat loading, morphology and adherence. A slurry coating technique was used to deposit. the alumina. layer onto t he monolit hs which were then subjected to ult.ra.sonica.t ion and thermal shock treatment. to test. for adherence. The active phase ,vas deposited by ion exchange and dry impregnation of the alumina coated monoliths by making use of a RuCb.xH"O solution. SEivI was employed to analyse the morphology of the layer, as well as its metal content and distribution. An experimental design soft,vare, Design Expert. was used to generate statistically significant and robust models for the results. It was found that washcoat loading, stability and morphology arc highly dependent on slurry solid content betvveen 20 and 45 v,rt.%, slightly affected by viscosity bet,veen 20 and 45 mPa.s and almost insensitive to pH beluw isoelectric point. Increasing slurry solid content results in an increase in washcoat loading which, in turn, results in thick and inhomogeneous layers which, in turn, arc more prone to cracking and to lo,v mcclmnical and thermal stability. The optimal point. that. gives a. st.able, homogeneous layer a.t the desired loading was identified to be at pH of 4, viscosity of 20 mPa.s and slurry solid content of 20 wt%. The resulting washcoat. layer is 'crack-free', uniform, and characterised by a washcoat loading of 10.8 wt%, an average thickness of 30 m, and mechanical and thermal weight losses of 0.79 and 1.42 wt%., respectively. The ion exchange techniques resulted in small and poorly distributed metal loading while dry impregnation resulted in sufficient metal loading and good distribution throughout t.he monolith channels.

Keywords

Chemical Engineering

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